Calf raises can be done using nothing but your legs and a surface to hold on to for balance, or you can kick it up a notch by using a stair.
I do these whenever I am in line at the grocery store, waiting for the bus, or just standing around my house.
"Stand tall with feet wider than the hips and toes turned outward. Hold onto the wall for support. Raise your heels up away from the floor and slowly lower them back down.
Exhale as you lift your heels and inhale as you lower down."